PROGRAM RandomNumber
! ------------------------------------------------------------------------------
!
! Copyright 2007 Matthew Norton
!
! ------------------------------------------------------------------------------
!    This program is free software; you can redistribute it and/or modify
!    it under the terms of the GNU General Public License as published by
!    the Free Software Foundation; either version 2 of the License, or
!    (at your option) any later version.
!
!    This program is distributed in the hope that it will be useful,
!    but WITHOUT ANY WARRANTY; without even the implied warranty of
!    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
!    GNU General Public License for more details.
!
!    You should have received a copy of the GNU General Public License
!    along with this program; if not, write to the Free Software
!    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
!
! NOTE: This is in FORTRAN 90 and you will need a FORTRAN 90 complier to run 
! this code
! ------------------------------------------------------------------------------
!
! This program calculates the derivative of cos(x) when it is evaluated at x = 1
! This program uses the 3-point, 2 point forward, 2 point backward, and the 
! 5-point approximation methods. This program also calculates the error 
! associated with each method.
!
! ------------------------------------------------------------------------------

IMPLICIT NONE
REAL :: GRandom, BRandom, GRand(10000), BRand(10000)
INTEGER :: I = 0, L = 0, ErrorStat = 0, NumofNum = 0, LL = 0
OPEN (UNIT = 20, FILE = "Random.txt", Status = "UNKNOWN", IOSTAT = ErrorStat)
IF (ErrorStat /= 0) THEN 
     STOP "*** Error in Opening File***"
END IF
L = 256
LL = 256
NumofNum = 10000
DO I = 1, NumofNum
     GRandom = GRandomNum(L)
     BRandom = BRandomNum(LL)
	      GRand(I) = GRandom 
     BRand(I) = BRandom
WRITE (20,*) I, GRandom, BRandom
WRITE (*,*) I, GRandom, BRandom
END DO
PRINT *, "Good Average:", SUM(GRand) / 10000.
PRINT *, "Evil Average:", SUM(BRand) / 10000.

! ------------------------------------------------------------------------------
CONTAINS
! ------------------------------------------------------------------------------
FUNCTION GRandomNum (L)
INTEGER, INTENT (INOUT) :: L
REAL :: GRandomNum

L = MOD(1366 * L + 150889, 714025)
GRandomNum = REAL(L) / REAL(714024)
RETURN
END FUNCTION

! ------------------------------------------------------------------------------
FUNCTION BRandomNum (L)
INTEGER, INTENT (INOUT) :: L
REAL :: BRandomNum
L = MOD(137 * L + 187, 256)
BRandomNum = REAL(L) / REAL(255)
RETURN
END FUNCTION
END PROGRAM RandomNumber